Since the past, a surface light source apparatus including a light guide panel has been used for purposes such as a backlight in liquid crystal display devices, internal illumination signboards, and lighting systems.
As a light guide panel used in this type of surface light source apparatus, in general, a light guide panel has been conventionally used that extracts light from a light source (such as a laser light source) towards the front surface side of the light guide panel using refraction or total reflection phenomenon attributed to the surface shape of the light guide panel having a grooved structure, a conical structure, a columnar structure, or the like.
On the other hand, a light guide panel using a diffraction grating has been proposed in recent years as a new type of light guide panel (refer to Patent Literature 1 and Patent Literature 2). This type of light guide panel has an advantage in that a surface light source having higher and more uniform luminance than that of the past can be actualized by transmission of light generated by diffraction by the diffraction grating.    Patent Literature 1: Japanese Patent Laid-open Publication No. Heisei 9-325218    Patent Literature 2: Japanese Patent Laid-open Publication No. Heisei 7-248496